Stabilized vacuum gap device with elementary electrode structure



Nov. 25. 1969 J. A. RICH 3,480,821

STABILIZED VACUUM GAP DEVICE WITH ELEMENTARY ELECTRODE STRUCTURE Filed Dec. 18, 1967 Fig. 2.

75 g2 In venfor Joseph A. Rm, 722 Line I by F M His Afforne y.

United States Patent Ofice 3,480,821 Patented Nov. 25, 1969 3,480,821 STABILIZED VACUUM GAP DEVICE WITH ELEMENTARY ELECTRODE STRUCTURE Joseph A. Rich, Schenectady, N.Y., assignor to General Electric Company, a corporation of New York Filed Dec. 18, 1967, Ser. No. 691,468 Int. Cl. H01j 1/02, 21/22, 35/28 U.S. Cl. 313148 8 Claims ABSTRACT OF THE DISCLOSURE Vacuum arc devices having a pair of oppositely-disposed arc electrodes of elementary configuration defining a single breakdown gap therebetween are stabilized by forming the electrodes in a hollow structure so that current is peripherally fed to the arcing faces. Due to the peripheral feed of current, the magnetic field in the interelectrode gap due to currents within the electrode interacts with the arc current to produce an inwardly-directed force upon the arc discharge so that the arc is stabilized and controllable. The are may be kept diffused, covering the entire arcing surface of the electrodes or may be caused to be constricted at the central portion of the electrodes, an important controlling factor being the distance between the arcing surface and the rear surface of each arc-electrode member.

The present invention relates to vacuum are devices including fixed gap vacuum devices and movable gap devices or vacuum switches wherein the arc electrode structure is elementary in structure, the simplest configuration being essentially plane-parallel. The present invention is related to my copending application, Ser. No. 639,693, filed May 19, 1967, as well as to the concurrently-filed, copending application of J. A. Rich and Willem F. Westendorp, Ser. 691,467, and assigned to the present assigne'e. The disclosures of the aforementioned applications are incorporated herein by reference thereto.

In my copending application Ser. No. 639,693, I set forth the fundamental precept which has indicated a new path in the development of controllable vacuum are devices. Briefly, the new concept in the development of such devices is related to the principle that the magnetic field component within the interelectrode gap in a vacuum arc discharge device that is perpendicular to the normal current conduction path between the arc-electrodes in the gap may be eliminated or made vanishingly small by causing opposite directions of current flow within the electrodes. In such vacuum arc devices, any magnetic field within the interelectrode gap which is perpendicular to the path of current within the gap causes an orthogonal force to be effective upon the are, such that for a unit of ionized plasma, the body force is defined by the relationship Since a fundamental limitation to thecurrent which may be carried in vacuum are devices is dependent upon the threshold for the formation of destructive anode spots, utilizing the aforementioned principles to control the body force upon current paths within an electric arc, may minimize the forces which tend to cause conduction paths to bunch up at a given point, causing a high density at the arc footpoints and the formation of anode spots.

The geometry of arc electrode devices to which the present invention relates is generally described as one in which the arc electrodes have plane-parallel configuration. Actually, this is an oversimplification and may vary from an exact plane-parallel configuration in which the arc electrodes are flat, completely parallel, generally disc shaped, and are separated by a narrow gap space, on one hand, to

the other extreme which may be found in a pair of opposed spherical, of hemispherical, arc-electrodes separated by a narrow gap. Most properly, this configuration is generally referred to as an elementary gap. In the normal elementary gap structures constructed in accord with the prior art, generally current is fed to and from the arcelectrodes centrally, so that under ideal symmetric conditions, the arc current causes the establishment of a magnetic field within the interelectrode gap that is azimuthal and symmetric with the longitudinal axis thereof. Any deviation from an exact centering of arc current conduction causes a bend in the arc path. A

force then acts upon the arc current path to cause it, and the ensuing arc, to be propelled rapidly to the periphery of the arc electrodes, at which point the arc hangs up and the current density rapidly increases to a point at which a destructive anode spot is formed, causing melting of the anode electrode.

Accordingly, it is an object of the present invention to provide vacuum arc device's having elemental gap configurations wherein the formation of anode spots at a given current is greatly minimized.

Yet another object of the present invention is to provide vacuum are devices wherein the arcing currents within the interelectrode gap are stabilized and rendered controllable.

Yet another object of the present invention is to provide vacuum arc discharge device's wherein peripheral hang up of arcs and the formation of anode spots thereby is minimized.

Still another object of the present invention is to provide vacuum arc discharge devices having substantially plane parallel electrode gaps configurations wherein a uniform distribution of current density between the arcelectrodes may be established and maintained.

Briefly stated, in accord with one embodiment of the present invention, I provide vacuum arc discharge devices having elementary arc-electrode configurations approximating a substantially plane-parallel configuration, wherein the arc electrodes are each hollow and current conduction occurs through an electrode support member that is centrally located to the rear of the electrode. Due to this configuration, current conduction paths within the electrode result in a peripheral current path and peripheral feed to the arcing surface of the electrode. The cumulative magnetic field due to the radially-outward current paths in the rear portion of the electrode and the radiallyinward current paths in the arcing surface of the electrode results in a partial cancellation of the component of the magnetic field Within the interelectrode gap which is perpendicular to the current conduction path therein (other than the self-induced magnetic field of the arc). By virtue of the controllable transverse remaining magnetic field, the conduction current paths with the interelectrode gap may be controlled so as to cover substantially the entire arcing surface of the arc-electrodes, or the arcing paths may be centrally constricted to cause the conduction arc paths to be centered at the central portion of the arc electrodes. The means by which the current flow paths are controlled is dependent, in part, upon size and shape of the electrodes, but primarily upon the distance between the arcing surface and the rear surface of the individual arc elec' trodes.

The novel features believed characteristic of the present invention are set forth in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the following detailed description, taken in connection with the appended drawing in which:

FIGURE 1 illustrates, in vertical cross section, a fixed gap vacuum discharge device constructed in accord with one embodiment of the present invention,

FIGURE 2 illustrates a variable gap vacuum are discharge device constructed in accord with another embodiment of the present invention, and

FIGURE 3 illustrates, in vertical cross section, yet another embodiment of the present invention.

In FIGURE 1, a triggerable vacuum gap device comprises a cylindrical insulating sidewall member and a pair of metallic endwall members 11 and 12, respectively. A pair of primary arc-electrodes 13 and 14, defining therebetween an interelectrode gap 15, are supported in oppositely-disposed relation to one another upon arc-electrodes support members 16 and 17, respectively, which are symmetrically connected to the center of the rear transverse electrode members 18 and 19, respectively. In addition to rear transverse electrode members 18 and 19, areelectrodes 13 and 14 include a relatively thick, arc-supporting transverse members 20 and 21, respectively, having arcing surfaces 22 and 23, respectively. Arc-supporting members 20 and 21 are connected to rear members 18 and 19 by means of cylindrical intermediate members 24 and 25, respectively. Thus, arc-electrode 13 comprises a transverse rear member 18, a substantially cylindrical sidewall member 24, and a transverse arcing member 20 having an arcing surface 22, defining a hollow cylindrical member. Similarly, arc electrode 14 comprises a rear transverse member 19, a transverse arcing member 21 having an arcing surface 23, and a sidewall member 25 connected therebetween. Arc-electrodes 13 and 14 are preferably fabricated from zone-refined copper or other high vapor pressure materials known to be suited to sustain a vapor arc in vacuo. Additionally, the arcing member 21 is apertured centrally, and a trigger electrode assembly 27, containing a trigger anode 28 and a trigger cathode 29, substantially as is illustrated in Lafferty Patent No. 3,323,002, for example, is centrally disposed therein, and an electric lead thereto is passed through a nonmetallic trigger lead member 30 which contains trigger anode connecting lead 31. The peripheral edges of the arc electrode surface members are rounded to prevent a preferred are footpoint at the periphery thereof so that well-known electric arc discharge phenomena will not cause the edges of such an unrounded configuration to become the preferred seat of the footpoint of an electric are.

In operation, the device is assembled and evacuated to a pressure of 10* torr or less. A high voltage of, for example, 50,000 volts is connected in circuit with the threaded ends of arc-electrode support members 16 and 17. A pulsed electric trigger voltage source is connected to trigger lead 31. A trigger pulse of microseconds duration which may have a magnitude of from 100 to 5000 volts, for example, depending upon the configuration of the gap and magnitude of the main voltage applied between the arc-electrodes, is supplied to trigger lead 31. A starter arc is established between trigger anode 28 and trigger cathode 29, which are moves out to the arcing sur face 23 of arcing member 21 of arc electrode 14, establishing a cathode spot thereupon. The main voltage is then broken down by the electron-ion plasma introduced into interelectrode gap 15 by the trigger arc and a plurality of discharge paths are established between arcing surfaces 22 and 23 of arc electrodes 13 and 14, respectively. In the normal, plane-parallel configuration of a vacuum arc, the following forces act upon the conduction paths which constitute the are between the two arc-electrodes.

As in all arcs, the fact that ionized particles are heated to a plasma temperature, causes a pressure gradient which results in a force tending to expand the plasma radially outwardly between the arcing surfaces.

Additional, any current path between arc-electrodes constitutes a vector quantity represented by the current density vector symbol J. Should there be any existing magnetic field within the interelectrode gap (other than the azimuthal field due to I) and should the field have a component B that is perpendicular to the conduction path within the arc, the conduction path has a body force acting upon it equal to the value where B is the component of the magnetic field that is perpendicular to the conduction path. In normal planeparallel electrode geometry, as would exist in the device of FIGURE 1, were the arc electrodes 13 and 14 solid, such a magnetic field would exist and would be substantially cylindrical about the longitudinal axis running through arc-electrode support members 16 and 17. Should any nonuniformity of current conduction occur at any point, other than on the exact longitudinal axis of the device, the expansive force due to the gas dynamics of the arc and the body force would be additive, and the arc would tend to move perpendicularly outwardly to the periphery of the arc electrode.

The technical and patent literature is replete with numerous illustrations of the normal tendency of an arc in a substantially plane-parallel configuration to be propagated to the periphery of the electrodes. Many elforts have been expended in seeking means for causing the arc to rotate about the periphery, so as not to cause a destructive anode spot to be formed by a substantially stationary reisdence of such an are at a given point. Other means are set forth to provide extended regions of anode and cathode emission so that the area of the anode and cathode spots is increased, thus decreasing the current density thereat.

In accord with the present invention, however, it is not necessary to take any such precautions. Thus, due to the peripheral feed of the current, which is along a conduction path which is radially outward on electrode members 18 and 21, and is longitudinal in interconnecting members 24 and 25 and peripherally fed to arcing members 20 and 21 and is radially inwardly in members 19 and 20, magnetic fields caused by radially outward and radially inward current conduction paths in the arc anode and are cathode, respectively (to the extent they are not cancelled out by oppositely-directed magnetic fields due to current paths in the remote portions of the electrodes) tend to impel non-symmetrical arcing paths toward the center of the interelectrode gap.

From my work I have determined that when. the distance between the forward transverse arcing member of the arc electrode and the rear center-fed transverse member of the arc electrode is only slightly less than the diameter of the arc electrode (assuming a disc-shaped electrode surface) that the component of transverse magnetic field perpendicular to the current-conduction path between the arc electrodes is primarily dependent on current conduction in the arc electrode arcing surfaces and less dependent on the current in the remote transverse member, to an extent that a force is exerted to constrain the arc plasma to the central region of the arc electrodes. This eliminates hang up at the periphery, thus permitting exceedingly high currents to be'obtained without causing the formation of destructive anode spots. It is important in the respect that the rear-most transverse member not be so far away as to have no effect, for if this were to occur, undue constriction would occur, leading to anode spot formation. In this mode of operation, any arclet which rises in current density, due to a localized condition, can form a separate anode spot, but the arclet is not propagated outwardly to the edge of the electrodes,

nor are the remaining conduction paths propagated to a peripheral point at which an exceedingly high-current density is achieved with destructive anode spot formation.

As the ratio of the diameter of the arcing surfaces to the distance between the forward and rear members of the hollow electrode members increases, the existing component of the magnetic field is less dominated by the current paths in the racing surfaces and the inwardly directed body force exerted upon the current conduction paths within the interelectrode gap is reduced, allowing the discharge to spread outwardly, under control, to cover substantially the entire arcing surface, permitting even higher total currents without increased current density. When, as is illustrated in FIGURE 1, the distance from the rear-most to the forward-most portion of the electrodes is approximately half the diameter of the arc-electrodes, the current conduction paths occupy approximately the center half of the parallel portion of the arc-electrode surface, a condition which is essentially ideal, in that all the current-carrying paths are of substantially equal length, corner effects are completely avoided, and the current density at any given point is not suflicient as to cause an undesirably low anode spot formation threshold current.

FIGURE 2 of the drawing illustrates a vacuum switch, or circuit interrupter, constructed in accord with the present invention. In FIGURE 2 an evacuable envelope includes an insulating cylindrical sidewall member 40 which separates the device into two electrically-insulated portions, and an upper and lower metallic end plate 41 and 42, respectively. A pair of arc-electrodes 43 and 44 are disposed within the envelope and define therebetween a breakdown gap 45. Arc-electrode 44 is mounted upon a movable support and actuating rod 47, while arc-electrode 43 is mounted upon a fixed support member 46.

Arc-electrode 43 includes a rear transverse member 48, a cylindrical sidewall member 54, and a forward relatively-thick arcing member 50 having an arcing surface 52. Arc-electrode 44 includes a rear transverse member 49, a cylindrical sidewall member 55, and a relativelythick arcing member 51 having an arcing surface 53. Contact is made between the arcing surfaces 52 and 53 by impelling arc-electrode support member 47 inwardly by means, not shown, compressing reciprocating bellows 58, which is mounted in reentrant flange portion 59 of end-wall member 42, to close an electric circuit. The electric circuit is opened and a vacuum are established between arcing surfaces 52 and 53 by a reciprocating motion of support member 47, withdrawing arc-electrode 44 from arc-electrode 43. This withdrawal of arc-electrode 44 from contact with arc-electrode 43 constitutes the means for establishing an electron-ion plasma within the vacuum gap between the arc-electrodes and is the functional equivalent of pulsing of trigger assembly 27 of the device of FIGURE 1.

The current conduction paths in the device of FIGURE 2 are essentially the same as that in the device of FIG- URE 1, and the same essential relationships govern, thus, the conducting plasma, containing a relatively-large number of conduction paths between arcing surface 52 and 53 is acted upon by a body force due primarily to the conduction paths in the arcing surfaces of the arc-electrodes which limits the discharge to the plane-parallel portions of the arc-electrodes, thus eliminating any possibility of edge effects.

FIGURE 3 of the drawing illustrates a device constructed in accord with the present invention wherein the configuration of the hollow arc electrodes is such as to reduce the force due to the surface currents by the proximity of the rear conducting members, thus permitting the arc discharge to spread evenly over substantially the entire surface of the arc-electrodes.

In FIGURE 3, an evacuable envelope includes a cylindrical insulated sidewall member 60 and upper and lower disc-shaped metallic endwall members 64 and 62, the latter of which is apertured to allow reciprocating motion of one arc-electrode. A pair of primary arc-electrodes 63 and 64, defining therebetween a substantially planeparallel discharge gap 65 are disposed within the envelope. Arc-electrode 63 is supported by electrode support member 66, which connects centrally with transverse rear member 68 of arc-electrode 63. Arc-electrode 64 is supported by electrode support member and actuating rod 67 which is centrally connected with rear transverse electrode member 69. Member 67 is reciprocably movable by means of hermetically-sealed bellows 75, which is connected on one end to actuating and support member 67 and on the other end, to a reentrant flange member 76, abutting the aperture in endwall member 62. As is indicated by FIGURE 3, the distance between transverse rear members 68 and 69, respectively, on one hand, and arcing members 70 and 71, on the other hand, is very small so that the magnetic field within the interelectrode gap due to radial currents therein greatly diminishes, but does not cancel the magnetic fields therein due to current conduction in the arcing members 70 and 71, which results in a moderate JXB force constraining the arc conduction paths to essentially all the arcing surfaces of arc-electrodes 63 and 64. This structure is utilized when it is desirable that a stable arc be formed at substantially all of the arc electrode with the lowest possible current density. It is apparent, however that utilizing this structure, the thickness of member 70 and 71 must be substantial, so as to avoid complete erosion therethrough. This criterion applies to all embodiments of the invention, of course. Similarly, in all embodiments the material from which the arcing members of the arc-electrodes are fabricated must be very pure, because the erosion thereof by the arc, would, if less pure material were utilized, cause the liberation of gas, which is inconsistent with the operation of a vacuum discharge device.

One device, functioning in accord with the invention, utilizes arc-electrodes that are substantially disc shaped With a three inch diameter and a one half inch radius bevel at the periphery thereof and having the distance between rear transverse members and forward arcing members approximately equal to one eighth inch and the thickness of the rear and interconnecting members approximately one eighth inch. The are which occurs upon separation of the arc-electrodes, as described with respect to the device of FIGURE 3, at a potential of 50,000 volts and a current of 30,000 amperes has a diameter of approximately 2.5 inches, which is desirable and does not cause damaging erosion of the surfaces of the anode 70 and the cathode 71.

In the embodiments illustrated in FIGURES 1-3, substantially plane-parallel electrodes have been illustrated for simplicity. It should be understood, however, that, as noted hereinbefore, the configuration of the arc-electrodes need not be exactly plane-parallel and may vary anywhere from the illustrated configuration to that of partially spherical or hemispherical arc electrodes. It is imperative in such variation, however, that the forward portion of the arc electrode which bears the footpoint of the electric are be of substantial thickness so that erosion thereof will not cause the arcing member to be penetrated. Similarly, the generalized relationship of the variation of the dimension between the forward and rear transverse members of the hollow electrodes with respect to the area of the arcing surface, of diameter thereof, as are set forth hereinbefore with respect to the substantially planeparallel geometry still governs although, quantitatively, the relationship may vary somewhat, depending upon the degree to which the electrode configuration approximates the substantially plane-parallel configuration.

Whatever the configuration, the greater the distance between the rear and forward members, be they parallel or curved in nature, the greater the force tending to constrain the arc within the central portion of the interelectrode gap. Conversely, the closer the two members are, the lesser the force tending to constrict the arc within the center of the interelectrode gap.

In all embodiments of the invention, the device is hermetically sealed and evacuated to a hard vacuum of the order of 10 torr or less. The arc-electrodes are fabricated of high-vapor pressure material such as zone-referred copper or other material such as is described in US. Patents 2,975,255, Lafferty; 2,975,256, Lee et al.; and 3,140,373, Horn, for example, and contain less than parts of gas and gas-forming impurities.

From the foregoing it is apparent that I have described a novel and useful configuration for vacuum arc devices, having either fixed or variable interelectrode gaps, wherein the arc-electrodes are peripherally fed with conduction current paths so that the magnetic fields within the interelectrode gap due to the conduction current paths within the electrodes may be controlled to stabilize and control the portion of the surface of the arc electrodes that is occupied by the arc discharge during operation. In one mode of operation, the rear and forward faces at the hollow arc-electrodes are very close together and the magnetic field, due to current conduction in the arcing face of the arc-electrodes, is partially cancelled by the field due to conduction in the rear conductor of the arc-electrodes, so that the arc substantially occupies all of the arcing surface of the arc electrodes without being forced to the periphery thereof, thus, providing for operation at high currents without the formation of destructive anode spots. In another mode of operation, the magnetic field may be regulated so that the resultant force upon the conduction is largely dominated by the current conduction in the arcing face members of the arc-electrodes and is such as to stabilize the arc and constrict it to a' relatively small central portion of the arc electrodes.

While the invention has been set forth hereinbefore with respect to certain specific embodiments thereof, many modifications and changes will readily occur to those skilled in the art. Accordingly, by the appended claims I intend to cover all such modifications and changes as fall within the true spirit and scope of the present invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A vacuum arc device adapted to support high current arcs therein and comprising:

(a) an hermetically sealed evacuable envelope at least a portion thereof being formed from an electrical insulator which separates said envelope into two electrically isolated portions;

(b) a pair of-arc-electrodes disposed within said envelope, each of said electrodes having an arcing surface adapted to sustain a footpoint of an electric arc discharge, and defining therebetween an interelectrode gap;

(b each of said arc-electrodes including (b a relatively thick arc-sustaining memher which includes said arcing surface (b a remote member including a central portion thereof adapted to supply electric current to said electrode, and (b means connecting said relatively thick arc sustaining member and said remote member at the respective peripheries thereof to define a hollow structure wherein current through said electrode is radially outwardly in said remote portion and radially inwardly along said relatively thick arcsustaining member, (b said current conduction paths in said areelectrodes being effective to provide a magnetic field within said interelectrode of gap which interacts with arcing currents to produce a radially inwardly directed body force thereon. so that arcing current paths between said arc-electrodes within said interelectrode gap are stabilized and controlled.

2. The device of claim 1 and further including means for supplying an electron-ion plasma within said gap to cause an electric arc between said arc-electrodes.

3. The device of claim 2 wherein said means for supplying an electron-ion plasma within said gap comprises a trigger assembly adapted to supply a trigger are when pulsed and wherein said arc-electrodes define a fixed gap.

4. The device of claim 2 wherein said means for supplying an electron-ion plasma within said gap comprises a movable arc-electrode reciprocably movable to engage the remaining arc-electrode and draw an electric arc therebetween when said arc-electrodes are separated.

5. The device of claim 2 wherein said arc-electrodes have substantially plane-parallel arcing surfaces with beveled edges.

6. The device of claim 2 wherein the distance between arcing surface in each electrode and said remote members is the appropriate transverse dimension of said arcing surfaces.

7. The device of claim 2 wherein the distance between said arcing surfaces in each arc-electrode and said rear member is approximately one half the transverse dimension of said arcing surface.

8. The device of claim 2 wherein the distance between said arcing surface and said rear transverse member in each electrode is very small as compared to the transverse dimension of said arcing surface.

References Cited UNITED STATES PATENTS 3,229,145 1/1966 Jensen 313-217 X 3,252,038 5/1966 Calvesbert et a1. 313-2l7 X 3,303,376 2/1967 Lafferty 313-233 X 3,323,002 5/1967 Lafi'erty.

3,345,484 10/ 1967 Polinko et al.

3,280,286 10/ 1966- Ranheim.

JAMES W. LA'WRENCE, Primary Examiner C. R. CAMPBELL, Assistant Examiner .U.S. CL X.R. 

